The present invention relates generally to keypad assemblies used in electronic devices such as mobile telephones, cordless telephone handsets, hand held computers, or the like, and more particularly to keypad assemblies employing touch detecting apparatus capable of sensing forces applied to keys of the keypad assembly for registering key presses.
Hand held electronic devices such as mobile telephones, cordless telephone handsets, hand-held computers, calculators, and the like, often employ keypads for entry of information and commands. FIG. 1 illustrates a traditional keypad assembly used in such devices. The keypad assembly 100 includes a circuit board 102 having a plurality of conductors 104. A keypad 106 is disposed over the circuit board 102. The keypad 106 includes a plurality of keys 108 consisting of resilient key domes 110, each providing a contact 112, positioned over a corresponding conductor 104 of the circuit board 102. When a force (F) is applied to a key 108 of the keypad 106, its key dome 110 is collapsed, bringing the contact 112 of the key dome 110 into contact with the corresponding conductor 104 disposed on the circuit board 102. This contact changes the electrical conductance of the conductor 104, registering a key press.
Traditional keypad assemblies employ a fixed key layout that is used for all input functions. Consequently, any new or different key assignments must be mapped to the existing key structure. This remapping of key assignments can cause confusion for the user of the electronic device employing the keypad assembly, and is limited by the original layout of the keys of the keypad assembly. Additional flexibility may be obtained by utilizing part of the display of the electronic device to provide key assignment choices to selected keys. This technique is used by the electronic device 200 illustrated in FIG. 2. The electronic device 200, in this case a mobile telephone, includes a housing 202 having a keypad assembly 204 and display 206. The keypad assembly 204 includes one or more dynamic function keys, 208 and 210, which are positioned directly below the display 206. The display 206, in turn, includes areas or regions 212 and 214 positioned adjacent to the function keys 208 and 210, that are used for displaying functions of the electronic device 200. In this manner, the function keys 208 and 210 may be used for selecting among various functions displayed in the regions 212 and 214. However, in most applications, the number of keys available for use as function keys is constrained by the space allotted on the display, since use of the display for displaying functions limits the display area that may be used for other purposes. Consequently, functions typically must be presented in a menu format, which many users find confusing.
In many applications, it would be desirable to provide an electronic device such as a mobile telephone, cordless telephone handset, or the like, having a single piece molded housing or shell, wherein the keyboard assembly is encapsulated within the material providing the housing. For example, electronic devices having this structure may often be manufactured at a substantially lower cost than devices having a conventional multi-piece housing and require less tooling and design time to produce. However, encapsulation of a traditional keypad assembly has proven problematic. As shown in FIG. 3, when a traditional keypad assembly 300 is encapsulated in a molded housing, resin is injected into the mold under pressure. As a result, one or more key domes 302 of the keypad assembly 300 may become collapsed. Due to the pressures exerted within the mold during molding of the housing 304, the subsequent depression 306 formed within the key dome 302 when it collapses becomes filled with resin, which sets and hardens, permanently holding the key dome 302 in the collapsed position. As a result, the keypad assembly 300 registers a continuous key press making the keypad assembly 300, and the electronic device containing the keypad assembly 300, unusable. Moreover, because the keypad assembly 300 is permanently encapsulated within the housing material of the electronic device, the electronic device typically cannot be repaired and must be discarded, resulting in unacceptable manufacturing waste when encapsulation methods are used.
Consequently, it is desirable to provide a keypad assembly for an electronic device such as a mobile telephone, a cordless telephone handset, a calculator, a hand-held computer, or the like, which utilizes touch detecting apparatus such as force sensors or touchpad assemblies instead of traditional key domes. The keypad assembly should be capable of encapsulation within the housing of the electronic device.